1. Field of the Invention
This invention relates to bowling pins and their manufacture and more particularly to wooden bowling pins having multiple layer external resinous or plastic coatings. More particularly still, the invention relates to bonding of separate layers of plastic coatings on bowling pins to each other.
2. Description of the Prior Art
It has been customary in the bowling industry to use bowling pins made of a hard shock resistant wood such as maple or preferably silver maple to resist the shocks and wear incident to being struck by bowling balls traveling at relatively high speeds and of significant weight, the usual pin weighing approximately three pounds and the usual bowling ball weighing between about 11 and 16 pounds depending upon the player. Moreover, since the contact surfaces of both the ball and the pin are convexly arcuate in configuration, the collision force between the two is exerted upon a relatively small area, or striking area, of the pin. As a result, very high shock forces are developed in the surface of the wooden pin. In addition, the relatively lighter pins, after being struck by the substantially heavier ball, attain very respectable recoil speeds, striking each other and portions of the alley pit with considerable force, further tending to damage the surface of the pin. As a result, the surface of the pin is subject to denting, chipping, pitting, and splintering as well as discoloration through abrasion and forceful imprinting into the pin surface of dirt and the like from the alley. Consequently, it has in the past been normal practice to refinish wood surfaces of bowling pins after as little as 200 to 300 games. In an attempt to alleviate these difficulties, plastic coatings and, particularly polystyrene outer plastic coatings or cladding, were in the past developed for bowling pins. This increased the life of the pin, which now could be used in favorable cases for one thousand games or more before having to be refinished or replaced. However, these polymeric clad pins also tended to be subject to the same difficulties at the surface of the pin as wooden surface pins with, however, the further problem of delamintion of the plastic coating from the surface of the underlying wooden core of the pin. Not only did the bond between the plastic coating and the hardwood core fail, but the wood itself also continued to fail as a result of crushing of the wood fibers. Once the wood fibers failed the surface coating of the pin would also not only fail itself, but become unattractive and essentially unusable.
All-resinous or solid plastic pins were also developed in the past. These were provided with a softer plastic core simulating wood and a harder plastic surface coating. Such previous pins, however, were subject to fracture of the surface coating and delamination of such coating from the core under the extreme shocks of the game exerted upon the surface of the pin and also were found to be deficient or unsatisfactory in other ways, such as, for example, making a sound upon impact unlike the sound of traditional wooden pins, which unnatural sound was frequently objected to by traditionalist bowlers. Solid plastic pins as well as some reinforced wooden pins also have not reacted or rebounded in the usual manner of wooden pins.
As a result of the foregoing difficulties, newer forms of coatings for wooden pins were developed in which an outer plastic coating was applied over a wooden core and a thinner hard abrasion and dirt resistant outer coating was adhered to the surface of the intermediate plastic coating by use of an epoxy-type intermediate bonding agent or adherent. One of the most successful of these coating systems has been the use of a so-called ionomer resin cladding such as described in U.S. Pat. No. 4,445,688 issued May 1, 1984 to Frillici and Infantino. To protect the surface of the ionomer cladding or coating from surface abrasion and soiling in such bowling pin constructions, an outer, or top, coat of a clear film of polyurethane resin has preferably been used, which outer coating has been adhered to the ionomer cladding with an epoxy or the like adhesive or bonding agent. Such top coats have been used to impart dirt and abrasion resistance to the underlying ionomer coating or cladding. Such top coats have customarily been between 0.0005 to 0.005 inches in thickness and sufficiently hard to resist dirt and soiling, but also must be sufficiently soft to be crack resistant or flexible to impact. Such outer coating should also be matched in flex resistance with the underlying ionomer resin. Furthermore, such outer coating must be well adhered to the underlying ionomer resin to prevent delamination during impact. So-called epoxy resins which typically are aromatic polyether polyepoxides, typically in turn reaction products of aliphatic glycols and epichlorohydrin, have been used to bond the outer thin polyurethane coating to the underlying ionomer coating. A wide variety of suitable curing agents such as primary and secondary aliphatic amines may be used with these epoxy bonding agents, the aim being to secure an adhesive "grip" or attachment between the underlying ionomer, and the outer polyurethane. A suitable ionomer for the primary coating is an ionic copolymer between an unsaturated alpha-olefin of from 2 to 10 carbon atoms with an unsaturated carboxylic acid having from 3 to 8 carbon atoms, plus optionally other monoethylenically unsaturated ionomers, with the copolymers having from 10% to 90% of the carboxylic acid groups in the form of a salt with metal ions, uniformly distributed throughout the copolymer. The outer polyurethane can have various compositions as long as it has a general flexibility or flex index similar to the ionomer and a hard stain-resistant surface.
Since it is important that the outer clear polyurethane film coating be securely bonded to the underlying ionomer cladding to prevent delamination and instantaneous or subsequent rupture of the film or top coat upon subjection to the rigorous shocks and stresses to which bowling pins are inherently subject, it is natural that one of the modern world's most versatile and frequently used bonding substances, i.e. epoxy resins, be used to secure the two together. However, there are difficulties. The epoxy components, i.e. the primary epoxide and the curing agent are applied as two component organic solvent based epoxy solutions. These organic base solvent solutions require large amounts of volatile organic compounds, which volatiles are very difficult to keep from escaping into the atmosphere with general environmental and working environment repercussions. It is particularly difficult to avoid contact of volatile organic compounds with the workers involved with manufacturing the plastic clad bowling pins. In addition, the ultimate bond strength is affected by the age and state of cure of the primer or epoxy bonding agent. Consequently, it is difficult to attain a uniform adhesion or bonding of the top or outer coat or film of polyurethane to the underlying ionomer cladding unless the bonding solution is rather frequently changed, which is difficult under the usual industrial plant conditions, even though having a critical degree of bonding of the two coatings is very important for preventing delamination after the pins are used in several thousand bowling games. Attempts have been made to find other effective bonding agents among the more usual bonding-type substances. However, the epoxy bonding system used for adhesion between the initial cladding with an ionomer and a thin outer film of polyurethane continues to be the standard bonding used in the industry. There has been a continuing need, therefore, for a better bonding arrangement or medium between the ionomer and the outer polyurethane coating on plastic-coated bowling pins.
The present inventor has unexpectedly discovered that two substances, namely a single component dilute water based solution of a polyfunctional aziridine or a polyfunctional carbodiimide can be substituted for the organic solvent based two component epoxy system presently being widely used. The bonding process and appurtenant processing equipment are thereby simplified and the bonding results are improved, all at a decreased cost and benefit to the environment.